1. Field of the Invention
The present invention relates to a coil component and, more particularly, to a terminal electrode structure of a surface-mount type coil component.
2. Description of Related Art
Along with recent miniaturization of electronic devices, a coil component is required to foe mounted in high density, as other components are required to do so. For example, Japanese Patent Application Laid-Open No. 2009-117627 discloses a surface-mount type coil component capable of achieving high density mounting.
This coil component includes a core having a winding core and flanges, an insulating case in which an accommodation space for accommodating the core is formed, a terminal electrode made of a metal fitting and mechanically fixed to the case in a state where at least a part thereof is exposed outside, and a winding (wire) connected to the terminal electrode and wound, around the winding core via the case. The accommodation space for the core is defined by including a bottom surface substantially parallel with a mounting surface. The winding core and flange have a lower surface of the winding core and a lower surface of the flange, respectively, which are opposed to the bottom surface of the case. The lower surface of the winding core is in the same plane as the lower surface of the flange. A leg portion protruding toward the mounting surface is defined in a position opposite to the flange of the case, and a mounting portion of the terminal electrode is arranged in the leg portion.
In the above-described coil component, the wire end terminal electrode are connected in such that a leading end section of the wire is thermocompression-bonded on the terminal electrode. When the wire is thermocompression-bonded on the terminal electrode, a material (Cu) of the wire and a plating film (Ni and Sn) on a surface of the terminal electrode react with each other to form an alloy layer. The alloy layer has a high melting point, so that when a portion of the alloy layer serves as a solder bonding surface upon mounting of the coil component on a circuit board, solder wettability may be lowered. Particularly, as illustrated in FIG. 9A, when a leading end section 20e of a wire 20 to be thermocompression-bonded is made to be aligned to an end portion of a terminal, surface of a terminal electrode 21, the alloy layer is formed from end to end of the terminal surface in a wire extending direction, that is, formed over a wide area of the terminal surface and, at the same time, a plating thickness of a side electrode is reduced, which may inhibit formation of a solder fillet to cause mounting failure.
To solve this problem, as illustrated in FIG. 9B, the leading end section 20e of the wire 20 is made to be aligned not to the end portion of the terminal surface of the terminal electrode 21, but to a position (in the vicinity of a center of the terminal surface) inward from the end portion. In this case, the wire 20 led out from the winding core of the core passes the terminal surface of the terminal electrode 21 to be led frontward thereof in the wire extending direction. Then, a wire section (section denoted by a continuous line) located rearward (in the wire extending direction) of a position to be set as the wire leading portion is thermocompression-bonded, and a front wire section (section denoted by a dashed line) in the wire extending direction is out for removal. However, if the front wire section is brought into contact with the terminal surface of the terminal electrode 21, the wire is disadvantageously fixed to the surface of the terminal electrode 21 due to melting of the plating film on the surface of the terminal electrode by heat generated upon the thermocompression bonding, making it difficult to cut and remove the front wire section. Such a problem occurs not only when the metal fitting is used as the terminal electrode, but also when a printed electrode is used as the terminal electrode, and there is required a countermeasure against this problem.